A monoclonal “antibody cocktail” drug developed by U.S. firm Regeneron Pharmaceuticals Inc. obtained fast-track approval from the Japanese health ministry on Friday for use as a post-exposure prophylaxis to prevent the spread of the coronavrius within households and for the treatment of asymptomatic COVID-19 patients.

Ronapreve, which is composed of the artificially produced antibodies casirivimab and imdevimab, was also given approval to be administered by subcutaneous injection, in addition to the intravenous injection that was already authorized, to provide flexibility in how the drug is given to match each patient’s needs. The approvals came a day after the ministry’s expert panel backed the treatment and mark the country’s first OK for a COVID-related drug to be used for prophylactic purposes, aside from the COVID-19 vaccines.

A global final stage clinical study assessing the efficacy and safety of Ronapreve in preventing symptomatic infection in household contacts showed that the drug reduced the risk by 81.4% in those who were not infected when they entered the trial.

The study also showed that Ronapreve reduced the risk of recently infected asymptomatic patients progressing to a symptomatic illness by 31.5%, said Chugai Pharmaceuticals Co., which has obtained exclusive commercialization rights in Japan from Roche, the drug’s Swiss co-developer.

In July, Ronapreve received Japan’s first authorization for the treatment of mild to moderate symptoms in people age 12 and above who do not require oxygen and are at a higher risk of their condition becoming severe. A clinical trial involving COVID-19 patients with a high risk of developing serious symptoms, such as those who are obese or have high blood pressure, had shown that the drug reduced the risk of hospitalization or death by 70.4%.

Subsequent clinical trials have backed its effectiveness in preventing infections in people who have had close contact with others, prompting Chugai Pharmaceuticals to file for approval for its expanded use on Oct. 11. But the drug is no substitute for the COVID-19 vaccines, the health ministry said.

Prime Minister Fumio Kishida visits the Tokyo Metropolitan Bokutoh Hospital, a general hospital accepting COVID-19 patients, in Tokyo on Oct. 9. | KYODO
Prime Minister Fumio Kishida visits the Tokyo Metropolitan Bokutoh Hospital, a general hospital accepting COVID-19 patients, in Tokyo on Oct. 9. | KYODO

“The trials were conducted on people who came into close contact with infected individuals, and its efficacy in preventing infections in anyone who has not had a close contact has not been confirmed,” a health ministry official said. “So that’s different from the vaccine.”

So far, 4,100 hospitals have signed up to administer the drug, and it had been given to about 36,000 patients as of Oct. 20, the health ministry said. Because of limited supplies, the government plans to limit its expanded use to people who fit the following three criteria: household contacts of COVID-19 patients and recently infected asymptomatic patients; people who are at risk of developing a severe condition; and people who have not received a COVID-19 vaccine or are thought to have low antibody levels despite vaccination.

In the trials, Ronapreve was confirmed to be effective when administered to close contacts via subcutaneous injection. Hypodermic injections are given in four locations in the body, such as the stomach, upper arm and the thigh, but it does not take as long to administer as the 20 to 30 minutes required for intravenous injection.

Because subcutaneous injection does not result in an immediate elevation of the drug’s presence in the blood, it will be recommended that the treatment is administered intravenously to symptomatic patients, the health ministry official said, adding that it is up to doctors to decide how to give the drug.

“Sometimes it’s hard to find optimum veins for people with a high BMI (body mass index) to administer an intravenous drip injection,” the official said. “In that case, subcutaneous injection would be useful.”

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